Field of the Invention
The present invention relates to an airfoil geometry that can be suitably applied to a rotor blade or a stator blade of an axial compressor and, in particular, to an airfoil geometry that can reduce pressure loss by suppressing shock generated on a pressure surface PS (pressure side).
Description of the Related Art
When the velocity of an airflow entering a blade row of an axial compressor exceeds the speed of sound, since as shown in FIG. 5 in an air passage between two adjacent rotor blades of the blade row, one strong shock (1st passage shock) is generated from the leading edge LE of one rotor blade toward the suction surface SS (suction side) of the adjacent rotor blade, the airflow velocity on the suction surface SS of the rotor blade rapidly decreases immediately after the 1st passage shock, and not only does pressure loss increase, but there is also the problem that the compression efficiency of the compressor is degraded due to boundary layer separation on the suction surface SS of the rotor blade being induced by the 1st passage shock.
In order to solve such a problem, the airfoil geometry of a rotor blade of an axial compressor disclosed in Japanese Patent Application Laid-open No. 8-254156 is provided with a concave region, which has a negative curvature, at a position close to the leading edge LE of the suction surface SS, and the position of a bottom portion (a portion that is most depressed) of the concave region is set within a range of 0% to 70% of the chord length from the leading edge LE. In accordance with this arrangement, a plurality of weak compression waves are generated along the suction surface SS (suction side), so that the magnitude of the 1st passage shock can be moderated, deceleration of the airflow velocity is made gentle, and it thus becomes possible to reduce the pressure loss on the suction surface SS of the rotor blade and suppress boundary layer separation.